This invention relates to an improvement in a crime preventive optical door viewer which may be set through a door or the like, whereby an observer may, from inside of the door, view a person or object on the outside of the door within the field of vision.
Conventionally, a house, a hotel or an office, may be equipped with a door viewer to enable surveillance of visitors or the like and to operate for prevention against crime. However, because of structural requirements, very complex steps may be involved in manufacturing and assembly of such door viewers. In this regard, it is well known that a conventional door viewer is comprised of two objectives and one eyepiece, and that the conventional construction utilizing an outer tube extending through the wall of the door is set by means of a threaded inner sleeve, a threaded tube and a "C" shaped spring without binding agents. Furthermore, other fixing means for both members of the conventional door viewer for attaching of both flanges of the inner and outer tubes provides a male screw on the outer surface of the inner tube and a female screw on the inner surface of the outer tube. Thus, both flanges are exposed from the surface of the door, and both tubes are threaded on the above stated screw.
U.S. Pat. No. 4,082,434 to Hayashi et al discloses a wide-angle optical system for a door viewer which includes an inner sleeve illustrated in FIG. 1 of that patent wherein the optical system of the two objective lenses and one eyepiece is assembled with each inner and outer tube and the inner sleeve. The concave objective lens 11 has a front convex surface 14 and a rear concave surface 15, and the intermediate concave lens 12 has a front concave surface 16 and a rear flat surface. It is generally recognized that the inner sleeve or the lens tube 118 operates only as a stopper of the second objective lens as indicated from an embodiment illustrated in FIG. 7, since a convex lens 113 is appropriately positioned in the inner sleeve 118 or the like to coincide with both focal points F.sub.1 and F.sub.2.
U.S. Pat. No. 4,116,529 discloses a wide-angle spyglass comprising three lenses, a threaded inner sleeve and a threaded cylindrical member and a C-shaped spring for a stopper of an eyepiece. The wide-angle lens 15 has a front convex surface 16 and a rear concave surface 17, and the objective 18 has a front concave surface and a rear flat surface. The threaded inner sleeve operates concurrently as the lenses stopper and an inner tube for connection in an outer sleeve, since an objective is firstly fitted in the barrel member before the inner sleeve and its fixture member is mounted to the barrel member.
Japanese Utility Model Publication No. 22057/1971 discloses a wide-angle door scope which includes an embodiment illustrated in FIG. 2 of that Utility Model Application wherein four lenses are assembled in the inner sleeve. The first dispersing lens 10 has a front convex surface 14 and a rear concave surface 15, the second concave lens 11 has a front flat surface 17 and a rear concave surface 19, and the third concave lens 12 has a front concave surface 21 and a rear flat surface 22 respectively. Also an eyepiece is resiliently fixed on the inner perpheral surface of the inner sleeve. It is generally recognized that the inner sleeve operates as the lens stopper and a fixing member thereof in an outer sleeve.